Coupled Double Optical Stark Effect in CdSe Colloidal Nanoplatelets

Optical Stark effect (OSE) is a coherent phenomenon that is in close relation to quantum information science and ultrafast optical modulation. Recent studies have demonstrated strong OSE from emerging semiconductor materials such as transition metal dichalcogenide monolayers, colloidal quantum dots, and two- and three-dimensional lead halide perovskites. A simple two-level model is often assumed for these materials, which could be oversimplied since there are many coupled transitions in semiconductors. Here we report the observation of the "double-OSE" in CdSe colloidal nanoplatelets arising from intercoupled heavy- and light-hole excitons that share the same conduction band level. The spin-selection rules associated with these two transitions led to strong OSE shifts of both transitions at room temperature under both co- and counter-circularly polarized pump/probe configurations, which is distinct from the conventional two-level OSE. The double-OSE not only deepens our understanding of the light–matter interaction in colloidal nanoplatelets, but also is potentially useful for novel optical modulation or information processing technologies.